By incorporating digital control systems for ignition of, and to some extent for fuel injection in, small internal combustion engines, opportunities have been created for the connection of external computers, in order thereby to be able to change the characteristics of the control system, as well as to be able to read operational data from the same. The implementation of a communication with an external computer is however associated with a number of restrictions, of which a low production cost and a high reliability are the most important ones. Such restrictions create problems in using communication solutions of today.
U.S. Pat. No. 5,210,846 discloses a one-wire bus for two-way communication. The basic principle of this two-way one-wire bus is good, but for technical reasons it is in practice inapplicable for internal combustion engines. This is because in this application, the described one-wire must be able to transfer power for feeding the control system during communication, and also the interface must include an extremely effective protection against voltage transients, since it is in the nature of an ignition system that it includes risks of unwanted discharges.
U.S. Pat. No. 6,549,843 discloses an internal combustion engine that may be used in an outboard engine, having an associated control unit. A general service computer can be coupled to ECU via a serial cable on the electronic control unit.